Figure 15.23a

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Epiglottis
Palatine tonsil
Lingual tonsil
Foliate papillae
Fungiform papillae
(a) Taste buds are associated with fungiform,
foliate, and circumvallate (vallate) papillae.
Figure 15.23a
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Circumvallate papilla
Taste bud
(b) Enlarged section of a circumvallate
papilla.
Figure 15.23b
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Structure of a Taste Bud

• Flask shaped
• 50100 epithelial cells
• Basal cellsdynamic stem cells
• Gustatory cellstaste cells
• Microvilli (gustatory hairs) project through a
  taste pore to the surface of the epithelium

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Connective tissue
Gustatory hair
Taste fibers of cranial nerve
Stratified squamous epithelium of tongue
Gustatory (taste) cells
Taste pore
Basal cells
(c) Enlarged view of a taste bud.
Figure 15.23c
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Taste Sensations

• There are five basic taste sensations
• Sweetsugars, saccharin, alcohol, and some amino
  acids
• Sourhydrogen ions
• Saltmetal ions
• Bitteralkaloids such as quinine and nicotine
• Umamiamino acids glutamate and aspartate

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Physiology of Taste

• In order to be tasted, a chemical
• Must be dissolved in saliva
• Must contact gustatory hairs
• Binding of the food chemical (tastant)
• Depolarizes the taste cell membrane, causing
  release of neurotransmitter
• Initiates a generator potential that elicits an
  action potential

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Taste Transduction

• The stimulus energy of taste causes gustatory
  cell depolarization by
• Na influx in salty tastes (directly causes
  depolarization)
• H in sour tastes (by opening cation channels)
• G protein gustducin in sweet, bitter, and umami
  tastes (leads to release of Ca2 from
  intracellular stores, which causes opening of
  cation channels in the plasma membrane)

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Gustatory Pathway

• Cranial nerves VII and IX carry impulses from
  taste buds to the solitary nucleus of the medulla
• Impulses then travel to the thalamus and from
  there fibers branch to the
• Gustatory cortex in the insula
• Hypothalamus and limbic system (appreciation of
  taste)

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Gustatory cortex (in insula)
Thalamic nucleus (ventral posteromedial nucleus)
Pons
Solitary nucleus in medulla oblongata
Facial nerve (VII)
Vagus nerve (X)
Glossopharyngeal nerve (IX)
Figure 15.24
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Influence of Other Sensations on Taste

• Taste is 80 smell
• Thermoreceptors, mechanoreceptors, nociceptors in
  the mouth also influence tastes
• Temperature and texture enhance or detract from
  taste

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The Ear Hearing and Balance

• Three parts of the ear
• External (outer) ear
• Middle ear (tympanic cavity)
• Internal (inner) ear

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The Ear Hearing and Balance

• External ear and middle ear are involved with
  hearing
• Internal ear (labyrinth) functions in both
  hearing and equilibrium
• Receptors for hearing and balance
• Respond to separate stimuli
• Are activated independently

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Middle ear
Internal ear (labyrinth)
External ear
Auricle (pinna)
Helix
Lobule
External acoustic meatus
Pharyngotympanic (auditory) tube
Tympanic membrane
(a) The three regions of the ear
Figure 15.25a
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External Ear

• The auricle (pinna) is composed of
• Helix (rim)
• Lobule (earlobe)
• External acoustic meatus (auditory canal)
• Short, curved tube lined with skin bearing hairs,
  sebaceous glands, and ceruminous glands

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External Ear

• Tympanic membrane (eardrum)
• Boundary between external and middle ears
• Connective tissue membrane that vibrates in
  response to sound
• Transfers sound energy to the bones of the middle
  ear

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Middle Ear

• A small, air-filled, mucosa-lined cavity in the
  temporal bone
• Flanked laterally by the eardrum
• Flanked medially by bony wall containing the oval
  (vestibular) and round (cochlear) windows

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Middle Ear

• Epitympanic recesssuperior portion of the middle
  ear
• Pharyngotympanic (auditory) tubeconnects the
  middle ear to the nasopharynx
• Equalizes pressure in the middle ear cavity with
  the external air pressure

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Oval window (deep to stapes)
Semicircular canals
Entrance to mastoid antrum in the epitympanic
recess
Malleus (hammer)
Vestibule
Incu (anvil)
Auditory ossicles
Vestibular nerve
Stapes (stirrup)
Cochlear nerve
Tympanic membrane
Cochlea
Round window
Pharyngotympanic (auditory) tube
(b) Middle and internal ear
Figure 15.25b
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Ear Ossicles

• Three small bones in tympanic cavity the
  malleus, incus, and stapes
• Suspended by ligaments and joined by synovial
  joints
• Transmit vibratory motion of the eardrum to the
  oval window
• Tensor tympani and stapedius muscles contract
  reflexively in response to loud sounds to prevent
  damage to the hearing receptors

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Epitympanic recess
Malleus
Incus
Superior
Lateral
Anterior
View
Pharyngotym- panic tube
Tensor tympani muscle
Tympanic membrane (medial view)
Stapes
Stapedius muscle
Figure 15.26
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Internal Ear

• Bony labyrinth
• Tortuous channels in the temporal bone
• Three parts vestibule, semicircular canals, and
  cochlea
• Filled with perilymph
• Series of membranous sacs within the bony
  labyrinth
• Filled with a potassium-rich endolymph

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Superior vestibular ganglion
Inferior vestibular ganglion
Temporal
bone
Semicircular ducts in semicircular canals
Facial nerve
Vestibular nerve
Anterior
Posterior
Lateral
Cochlear nerve
Cristae ampullares in the membranous ampullae
Maculae
Spiral organ (of Corti)
Utricle in vestibule
Cochlear duct in cochlea
Saccule in vestibule
Stapes in oval window
Round window
Figure 15.27
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Vestibule

• Central egg-shaped cavity of the bony labyrinth
• Contains two membranous sacs
• Saccule is continuous with the cochlear duct
• Utricle is continuous with the semicircular
  canals
• These sacs
• House equilibrium receptor regions (maculae)
• Respond to gravity and changes in the position of
  the head

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Semicircular Canals

• Three canals (anterior, lateral, and posterior)
  that each define two-thirds of a circle
• Membranous semicircular ducts line each canal and
  communicate with the utricle
• Ampulla of each canal houses equilibrium receptor
  region called the crista ampullaris
• Receptors respond to angular (rotational)
  movements of the head

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Superior vestibular ganglion
Inferior vestibular ganglion
Temporal
bone
Semicircular ducts in semicircular canals
Facial nerve
Vestibular nerve
Anterior
Posterior
Lateral
Cochlear nerve
Cristae ampullares in the membranous ampullae
Maculae
Spiral organ (of Corti)
Utricle in vestibule
Cochlear duct in cochlea
Saccule in vestibule
Stapes in oval window
Round window
Figure 15.27
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The Cochlea

• A spiral, conical, bony chamber
• Extends from the vestibule
• Coils around a bony pillar (modiolus)
• Contains the cochlear duct, which houses the
  spiral organ (of Corti) and ends at the cochlear
  apex

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The Cochlea

• The cavity of the cochlea is divided into three
  chambers
• Scala vestibuliabuts the oval window, contains
  perilymph
• Scala media (cochlear duct)contains endolymph
• Scala tympaniterminates at the round window
  contains perilymph
• The scalae tympani and vestibuli are continuous
  with each other at the helicotrema (apex)

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The Cochlea

• The roof of the cochlear duct is the vestibular
  membrane
• The floor of the cochlear duct is composed of
• The bony spiral lamina
• The basilar membrane, which supports the organ of
  Corti
• The cochlear branch of nerve VIII runs from the
  organ of Corti to the brain

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Modiolus
Cochlear nerve, division of the vestibulocochlear
nerve (VIII)
Spiral ganglion
Osseous spiral lamina
Vestibular membrane
Cochlear duct (scala media)
Helicotrema
(a)
Figure 15.28a
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Vestibular membrane
Osseous spiral lamina
Tectorial membrane
Spiral ganglion
Scala vestibuli (contains perilymph)
Cochlear duct (scala media contains endolymph)
Stria vascularis
Spiral organ (of Corti)
Scala tympani (contains perilymph)
Basilar membrane
(b)
Figure 15.28b
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Tectorial membrane
Inner hair cell
Hairs (stereocilia)
Afferent nerve fibers
Outer hair cells
Supporting cells
Fibers of cochlear nerve
Basilar membrane
(c)
Figure 15.28c
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Inner hair cell
Outer hair cell
(d)
Figure 15.28d
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Properties of Sound

• Sound is
• A pressure disturbance (alternating areas of high
  and low pressure) produced by a vibrating object
• A sound wave
• Moves outward in all directions
• Is illustrated as an S-shaped curve or sine wave

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Area of high pressure (compressed molecules)
Area of low pressure (rarefaction)
Wavelength
Air pressure
Crest
Trough
Distance
Amplitude
A struck tuning fork alternately compresses
and rarefies the air molecules around it,
creating alternate zones of high and low
pressure.
(b) Sound waves radiate outward in all
directions.
Figure 15.29
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Properties of Sound Waves

• Frequency
• The number of waves that pass a given point in a
  given time
• Wavelength
• The distance between two consecutive crests
• Amplitude
• The height of the crests